Autogenous grinding process and mill systems to perform the same



Feb. 19, 1963 H. HARDINGE 3,078,059

AUTOGENOUS GRINDING PROCESS AND MILL SYSTEMS TO PERFORM THE SAME FiledJan. 8, 1960 5 Sheets-Sheet l 452 Z /76 /64 F/s. Ma

Q INVENTOR ATTORNEY Feb. 19, 1963 Filed Jan. 8. 1960 H. HARDINGE3,078,050 AUTOGENOUS GRINDING PROCESS AND MILL SYSTEMS TO PERFORM THESAME 5 Sheets-Sheet 2 INVENTOR /qELOk E HQQO/A/GE ATTORNEY Feb. 19, 1963H. HARDINGE 3,078,050

AUTOGENOUS GRINDING PROCESS AND MILL SYSTEMS TO PERFORM THE SAME FiledJan. 8, 1960 5 Sheets-Sheet 3 INVENTOR HQELOt/E A/neo/A/az ATTORNEY Feb.19, 1963 H. HARDINGE AUTOGENOUS GRINDING PROCESS AND MILL SYSTEMS TOPERFORM THE SAME 5 Sheets-Sheet 4 Filed Jan. 8, 1960 INVENTOR #4240: #4

Feb. 19, 1963 H. HARDINGE 3,078,050

AUTOGENOUS GRINDING PROCESS AND MILL. SYSTEMS TO PERFORM THE SAME FiledJan. 8, 1960 5 Sheets-Sheet 5 I NV EN TOR A/GELOh E gleam/v05 BY KATTORNEY United rates ldatent 3,97%,9553 AUTGQ-ENGUS GRENEENG PROCESE:AND Mill SYSTEMS TU PERFGRM THE SAME Harlote Hardinge, 24d Areh Sti,Yorh, Pa. Filed lion. 8, 1964 Ser. No. 1,291 Claims. (Cl. 241-26) Thisinvention relates to improvements in a grinding process and a number ofembodiments of mill systems capable of performing the same and, moreparticularly, to the utilization of tumbling type mills, of whichautogenous grinding mills are one preferred type, to perform novelprocedural steps and employ novel structure to achieve such proceduralsteps.

Heretofore in the employment of tumbling type mills and particularlyautogenous grinding mills, wherein runof-the-mine friable material isfed to the mill and actually grinds itself, it has been found in manysituations, which depend largely upon the type of material being treatedby the mill, that an undesired excess of relatively large lumps,pebbles, or cobs were produced and, as a result of this, reduced thegrinding efliciency of the mill system. Further, in many situations, thegrinding efiiciency, particularly of an autogenous grinding mill, can beimproved if the relative proportions of various ranges of sizes offriable material can be maintained substantially in a predeterminedproportion which has been found to produce maximum efiiciency inproducing fine products within desired ranges, for example, from acertin material fed to the mill in run-of-the-mine condition. in usingknown types of tumbling mills and particularly autogenous type grindingmills heretofore, it has not been possible to produce such predeterminedand desired proportions of various ranges of sizes of friable materialwithin the mill to effect maximum efiiciency in producing a desiredrange of fine materials which ultimately are discharged from the mill.

To overcome the difficulties and deficiencies of existing and previouslyused systems and processes for grinding solid friable material to reducethe same to desired ranges of fine material, as well as to effect othereffi iencies and improvements in the reduction of solid friablematerials to desired ranges of fine sizes, preferably by the use ofgrinding mills and even more particularly by the use of autogenousgrinding mills, it is the principal object of the present invention toprovide a novel and eiiicient process of grinding solid friable materialpreferably by the use of a primary and one or more secondary grindingmills comprising a grinding system which operates substantially as aunit and has inter-related feeding, segregating and classifyingmechanism which may be operated either manually or automatically, toeffect desired adjustment and control of the operation of said millsystem to produce a maximum amount of a desired range of sizes andparticularly fine sizes of product material at minimum operationalcosts. The term solid friable material, as used herein, is considered tobe material of varying degrees of hardness which can be broken bytumbling action and the word friable is considered to be generic tocover a wide range and classes of mineral materials which are capable ofbeing processed in accordance with the principles of the presentinvention.

Another object of the invention which is a corollary of the foregoingobject is to employ the friable material being ground either in part orin whole as the grinding media and so arrange the distribution of saidmedia in the primary and secondary mills, either manuall orautomatically, so as to obtain optimum results in the circuit comprisingall of the mills employed therein.

A still further object of the invention which is at least somewhatcorollary to the foregoing objects is to employ a primary mill in theoverall mill system which is utilized free to reduce the coarserfraction of the friable material fed thereto and some or all of theproducts of said primary mill then are fed in predetermined desiredproportions of ranges of different sizes to other grinding means whichmay be considered secondary or re-grinding mills, and also provide meansto regulate the feed of material between the various mills in such amanner that, as the friable grinding media obtained from the primarymill is consumed by the re-grinding processes effected in the secondarymills, the required grinding media therefor is replenished from the mainfeed supply source or from the primary mill, such supply beingcontrolled either manually or automatically as dictated by the operatingconditions in either the primary or secondary mills, or both.

Still another object of the invention is to utilize in theabove-described secondary or re-grinding mills of the foregoing objectsthe excess of pebbles produced in the primary mill, which pebblesusually are quite well rounded so as to render them ideal as pebble typegrinding media, in predetermined, controlled quantities in the secondaryor re-grinding mills of the grinding system.

A still further object of the invention is to provide a process andvarious embodiments of mechanical arrangements to achieve the same forpurposes of removing, preferably continuously and at adjustable rates,from either the primary or secondary mills the product material producedthereby, classify the same into a plurality of desired ranges of sizes,and then utilize said ranges of sizes either in the primary or secondarymills by controlled feed which may if desired re-introduce some of thesizes back into the mill from which it is removed for purposes of eitherserving as grinding media or to be reduced further in size by largerpieces of grinding media, all of such operations being controlled eithermanually or automatically to effect maximum efiiciency in the overallmill system.

One other object of the invention is to provide in a mill system of thetype described above means for indicating and controlling the operatingconditions in a tumbling mill system, and preferably an autogenousgrinding mill system, composed of a plurality of inter-related grindingcomponents or mills, whereby the operating conditions of one componentor mill bears a relation to the operating characteristics of mill andalso including the utilization of this relationship to efiect maximumoverall efliciency in the operation of the mill system.

Details of the foregoing objects and of the invention, as well as otherobjects thereof, are set forth in the following specification andillustrated in the accompanying drawings comprising a part thereof.

In the drawings:

FIG. 1 is an exemplary side elevation, shown partly in vertical sectionto illustrate certain details, of a mill sys' tem embodying theprinciples of the present invention and capable of performing a grindingprocess in accordance with the principles of the invention.

FIG. 2 is a substantially diagrammatic mill system shown in verticalelevation on a smaller scale than that employed in FIG. 1 and comprisinga different embodiment of mill system from that shown in FIG. 1.

FIG. 3 is an enlarged vertical elevation, partly in section toillustrate certain details, of an exemplary primary mill unit of thetype generally illustrated in FIGS. 1'

and 2.

FIG. 4 is a fragmentary sectional view of a detail of the mill unitshown in FIG. 3 as shown on the line 4-4 of said figure.

FIG. 5 is a fragmentary vertical sectional elevation of a portion of theprimary mill unit shown in FIG. 3 but in which a section of the lifterand clamping bar arrangeanother component or' ment has been removed toprovide exit means for a larger size of pebble or cob material thanwould be permitted by the arrangement illustrated in FIG. 3.

FIG. 6 is a fragmentary side elevation of the interior face of the millas seen on the line 6-6 of FIG. and illustrating four differentexemplary arrangements of exit space means respectively provided in thefour lifting and clamping bar arrangements shown therein.

FIG. 7 is a fragmentary transverse sectional view taken on the line 7-7of FIG. 5.

FIG. 8 is a fragmentary vertical sectional view of the exit, end of theexemplary primary mill illustrated in FIGS. 1 through 3 and utilizing alarger scale than in any of said figures to illustrate details of oneembodiment of segregating means for the material discharged from theexit, of said primary mill.

FIG. 9 is a vertical sectional elevation taken on the line 9-9 of FIG.8.

FIG. 10 is a vertical sectional elevation of another embodiment ofprimary mill structure and discharge meanswith still another embodimentof material segregating means which receives product material from theprimary mill, said mill and segregating means also embodying theprinciplesof the present invention.

FIG. 11 is a vertical elevation at 90 to the view shown in FIG. 10 asseen on the line 1111 of said figure, part of one end wall of theprimary mill being broken away in FIG. 11 to illustrate details of thetumbling of the material within said primary mill.

FIG. 12 is a diagrammatic view of an exemplary auto matic controlsystem, electrically actuated, for various adjustable operations ofcertain components of the mill systemsillustrated in theprecedingfigures.

Referring to the drawings, and particularly FIG. 1, an exemplary millsystem employing the present invention is illustrated therein, thisillustration being intended to be that of a typical mill circuit,principally to illustrate the basic principles of the invention, Such asystem, as illustrated, andalso in accordance with the principles ofthepresen-t invention, may be operated either as a wet or dry grindingmill system. Further,'the system may embody the principles of either aclosed or open circuit with screens or classifier system.

The mill system shown in, FIG.'1 essentially comprises a feed bin 10 forthe primary mill 12. Material of a friable nature to be treated is fedfrom the bin 10 by the feeder belt 16, in a so called run-of-mine orheterogeneous condition, through an adjustable outlet means 14. The feedbelt 16, for example, operates at a regulatable, desired speed tointroduce the raw material to entrance chute 18 of the primary-111111.12in controlled amounts. Said feed belt 16 is powered by suitable meanssuch as an electric motor '20 whereby, when the speed of the belt 16 andpossibly the adjustment of the outlet means 14 are regulated relative toeach other, a desired feed rate of raw material to the entrance chute 18is produced.

The primary mill 12 is preferably of the tumbling type and rotates abouttrunnions 22 positioned in suitable bearings, not shown, the mill beingpowered by drive gear 24 which is driven by suitable drive means toeffect a desired rotational speed of the primary mill 12 in accordancewith conventional operating practice for mills of this type.

Referring to FIG. 3,, it'will be seen that the mill 12 is illustrated ona larger scale than FIG. 1 and certain details of the interior of themill 12 are shown. Details and operational characteristics of this typeof mill are illustrated in applicants co-pending application Serial No.822,612, filed June 24, 1959. Specifically, but without intention torestrict the invention thereto, the mill 12 employs autogenous grindingprinciples. Aside from conventional lining plates, the interior of themill 12 is provided with deflecting rings 26 to insure substantialtransverse dispersion of the various ranges of sizes of the material asthe mill 12 is rotated about its axis for treatment of the raw friablematerial which is introduced through entrance chute 18.

Substantially radial clamping and lifting bars 28 are arranged at oneend of the mill, and these cooperate with transverse clamping andlifting bars 30 around the interior perimeter of the mill. The oppositeend of the mill is provided with an annular space 32 between thesegmental grate sections 34 and the outer end wall 36 of the mill. Thesegmental grate sections 34 are clamped in operative position by aseries of separable clamping and lifting bar sections 33 which aresecured by bolts 40 to the mill. The substantially radial iifter bars 38extend from the deflector rings 26 of the mill approximately to theouter perimeter thereof as is clearly shown in the lower portion ofFIGS. 3, 5 and 6. The lifter bars are spaced from each othercircumferentially.

As raw solid friable material which is to be treated is introduced tothe mill 12, it will be tumbled as a result of being elevated by therotation of the mill shell and various lifter bars. It will also bedeflected transversely and otherwise especially by the deflecting rings26 which extend inwardly from opposite ends of the mill. The largerlumps or cobs of said friable material will serve as grinding media toreduce the size of smaller particles of the material and, in turn, willgradually be reduced in size themselves in an autogenous mill. As thefriable material is gradually reduced in size to the width of the slots46 in the grate sections 34, said material will pass through said grateslots and thus be screened and sized as it moves into the annular space32 and then will be raised by the lifter plates 42 therein so that, whenelevated, the material will fall by gravity from the spaces between thelifter plates 42 and will be deflected by the exit cone 44 for dischargethrough the discharge cone 48.

In normal operation of a mill of this type, the width of the grate slots46 will serve as restricting means to control the size of the productmaterial discharged from the mill. However, in accordance with theprinciples of the present invention, assume by way of example only thatthe grate openings or slots 46 are Vs inch Wide. Similarly, assume thatthe radial spaces 5% between the edges of adjacent grate sections is ofthe order of 3 inches. Normally, these radial spaces 50 are closed bythe clamping and lifting bar sections 38. However, according to theprinciples of the invention, a predetermined number of the sections 38,at predetermined locations in the various slots 59 are removed inaccordance with one or more exemplary illustrations in FIG. 6 so as toprovide additional restricting discharge or exit spaces of predeterminedwidth and length to produce a desired variable discharge location andarea of such spaces through which a desired quantity of larger andpreferably rounded pieces of friable material having a maximum dimensionof 3 inches can pass, together with some intermediate and fine sizes ofsuch material, as illustrated in exemplary manner in FIG. 5. In thisfigure, the larger pieces 52 of material are shown respectively onopposite sides of the grate 34, one of these being in the space 32. Suchpieces 52 as well as those of intermediate and fine sizes which fallinto the space 32 will be discharged from the discharge cone .8 as themill 12 continues to rotate. Under normal circumstances however, inaccordance with the principles of the invention, the minus inch materialwhich passes through the grate openings or slots 46 will preferablycompose the major portion of the material discharged. In the event someauxiliary grinding media such as balls are employed in the primary mill,such media to be retained in the primary mill should be of a sizeexceeding the minimum dimension of the open spaces 56.

By referring to FIG. 6, it is to be understood that the four differentarrangements of spaces 50 and clamping and lifting bar sections '33shown therein principally are intended to be illustrative of differentexemplary arrangements of extentand position of open spaces 50 ratherthan being of the preferred manner of arranging such open spaces.However, if found advantageous, some such heterogeneous arrangement ofspaces may be utilized, as desired.

By virtue of the possibility of arranging the extent and positions ofthe open spaced sections 59 as shown in FIG. 6, the operator of the millcan determine by trial and error the desired selection of the mostefficient extent and location of such discharge spaces in order toprovide a desired discharge rate of minus 3 inch pebbles, for example,and such intermediate and fine sizes of materials as happen to passthrough the spaces 59. By way or" further illustration of the spaces 50,FIG. 4 is a sectional view showing the space 5t} closed by the clampingand lifting bar 38, while FIG. 7 shows an open space 5d resulting fromremoval of the bar section 38.

Reverting to FIG. 1 and also additionally referring to FIG. 8, themixture of material 54 exiting from the mill and consisting of ranges ofsizes from minus 3 inches, for example, of which the larger pieces 52represent the largest sizes, and on down to the minus /s inch sizeswhich have passed through the grate slots 46, are discharged into theclassifying or segregating mechanism or trommel 5'6.

Specifically, and particularly as illustrated in FIG. 8, the trommelmechanism 56 comprises an outer cylindrical screen 58 which preferablyis connected to the exit end of mill l2 and rotates therewith, as doesalso the inner cylindrical grate bar member 69' of the trommel. By wayof example only, assume that the screen 58 is 4 mesh, that is, somewhatless than /4 inch material may pass therethrough, and the parallel barscomprising the grate bar member are 1 inch apart. It will be seen fromFIG. 8 that the minus 4 mesh material 62 will be sifted through the barson and seem 58 and fall into hopper 64, while the minus 1 inch-plus 4mesh material 66 will not pass through the screen 58 but, rather, willbe discharged from the outer end thereof into another hopper 68.

Arranged internally of hopper n8 is still another hopper or sub-h0pperill which has a discharge chute 72. Flexibly connected at one end to oneside of the upper end of discharge chute i2 is an adjustable deflectorplate or splitter id which may be moved to any desired position in thechute, of which the various dotted line positions thereof shown in PlG.9 are exemplary, for purposes of intersecting the fall of a desiredamount or" the minus 3 inch-plus 1 inch material 52 as it is dischargedfrom the outer end of grate bar member 63, thereby controlling theamount of such material which will be discharged from hopper as into thelower end of material elevator 73, see PEG. 1, for return by gravitythrough conduit from the upper end of elevator "73 to the entrance chute13 of the mill for further reduction of size of such particles. Ifhowever the deflector plate or splitter '74 is extended to the right, asconsidered relative to PEG. 9, to its maximum intended position,substantially all of the minus 3 inch-plus 1 inch material will bedeflected into discharge chute 72 for one of several purposes, asfollows.

By referring to FIG. 1, it will be seen that the hopper e4 communicateswith a downwardly extending conduit 82 which communicates at its lowerend with entrance chute 84 of a secondary or regrind mill as which is ofa tumbling nature and is mounted on suitable trunnions 83 for rotationabout its axis, it being understood that the conventional bearingsemployed to support both the mills 12 and 86 are omitted in the variousfigures to simplify the illustration. Mill i6 is driven by conventionaldrive gear W- and a pinion gear X2. which is driven by suitable meanssuch as an electric motor 94.

It will therefore be seen that the system, if desired, can be operatedas a complete unit to the extent that no outside source of material orpebbles for the auxiliary or re-grind mill as are required. The overalloperation is simple and economical and subject to appreciablefiexibility. It is possible and very simple to change the size ofpebbles desired by changing, for example, the sizes of the openings 55}between the grate sections of the mill, as Well as the size dimensionsof the trommel screen 53 or grate bar member 69, either with or withoutadjustment of the deflector plate '74. It will be understood of coursethat all of these members need not be changed or adjusted in order toeffect a desired resulting product but it is desired to emphasize thatall of these possible adjustments are available, either singly or incombination with each other to effect the production of a desired rangeof products economically and with minimum power consumption.

Where the size ratio of friable material undergoing reduction variesconsiderably over an extended period of time and might require aconsiderable amount of adjustment of deflector splitter plate 74 the useof a surge bin l d may be desirable. Pebbles from the discharge chute'72 are deflected into the surge bin 93 by opening deflector plate orgate Nil. The friable pebbles are then fed to the mill 86 by a separatecontrolled rate feeder 152 in the quantity desired. While someadjustment of the quantity of pebbles cobbed from the system byregulating deflector plate 74 from time to time may be necessary, thisneed be done only over relatively extended periods of time, thus makingthe system more stable and easier to control.

Whereas the mill system arrangement shown in FIG. 1 can be considered aclosed circuit system by employing the elevator 7'8 and return conduit80, a so-called open circuit arrangement is shown, diagrammatically, inthe system illustrated in FIG. 2. in this embodiment, it will be assumedthat suitable feeding means are provided for supplying ratfriablematerial to the entrance of the tumbling mill 12. The exit of the mill12 substantially continuously discharges a mixture of product materialcomprising mostly relatively fine material which is suificiently line topass through the slots of the grate sections of the mill, this materialfor example, being of the order of minus inch. This material togetherwith relatively large sizes of minus 3 inch, for example, andintermediate sizes as controlled by adjusting and regulating the spaces59 between the grate sections of the mill, is all discharged either ontoor into suitable classifier or segregating means ill-lwhich results inthe exemplary coarse particles and lumps ranging from minus 3 inch toplus 1 inch size being discharged along the line 1% comprising conduitmeans, for example, discharging into surge bin 1558. The minus 1 inch toplus 4 mesh material is discharged into suitable conduit meansrepresented by line for introduction into the entrance end of another orthird tumbling mill '112 which, for example, may be a rod mill or apebble mill. If a rod mill is used, then metal rods will readily reducethe minus 1" portion to a size suitable for the secondary mill. If apebble mill is used, for example, then the use of larger pebbles such asminus 5" plus 3", cobbed directly from the mill feed, will serveadequately to reduce the minus 1" portion that is delivered to the thirdmill, which mill will accomplish similar results to a rod or ball millfor this size reduction range, as is wel llmown in the ant. Thus, byemploying this alternate method of reducing the minus 1" plus 4-rneshfraction so that is discharged through the spaces 50 and not of asuitable size for reduction in the secondary mill 116, it is possible toavoid the use of material elevator 78. In effect, this is an opencircuit operation to accomplish the same general end result as theclosed circuit arrangement of FIG. 1 which uses elevator '78 to returnthe minus 1" plus A" fraction to the primary mill. The minus 4 meshmaterial is discharged from segregating means 1G4 and travels alongother conduit means 114 to the entrance of secondary or re-grind mill116 of the tumbling type and similar, for example, to mill 8'6 shown inFIG. 1 both as to structure, operation, and function. It will be seenthat considerable flexibility is offered by the mill system shown inFIG. 2, due particularly to the inclusion of the intermediate grindingmill 112. The

product of this mill is so adjusted to approximate that desired as feedmaterial for the secondary mill such as, for example, minus 4 mesh size.When the material has been reduced to this size in intermediate mill112, it is discharged into the line 114 for feed to the secondary orre-grind mill 116.

To insure that the secondary mill 116 will have adequate grinding media,the accumulated larger size friable pebbles and cobs in surge bin 108are fed at a desired rate therefrom into the line 114 for introductioninto the secondary or re-grinding mill 116 and in which an overallproduct of a desired range of fineness is produced.

In referring to the various sizes of mesh and other sizes of productsproduced either finally or intermediately in the processes and millsillustrated in FIGS. 1 and 2, it is distinctly to be understood that thesizes which have been specifically recited solely are by way of exampleand are in no wise to be considered as restrictive of the presentinvention to these sizes. A relatively wide range of sizes is capable ofbeing used in and produced by the mill systems described above and,illustrated in FIGS. 1 and 2, all within the spirit of the presentinvention.

Referring now to the embodiment shown in FIGS. and ll, a tumbling mill118 is provided which is somewhat different from mill 1'. shown in FIGS.1 and 2 for example. Mill 118 is a primary mill and, is intended as inthe previously described mill to be illustrative of an autogenousgrinding type as well as one which may also employ some auxiliarygrinding bodies such as steel balls, whereby the same is provided withradial lifting bars 120 on the opposite ends of the mill and transverselifting bars 122 on the internal periphery of the primary mill 118.Conical, annular deflecting rings 123 also may e employed to insurethorough intermix-ing of all ranges of sizes of the materialwhile beingground within the mill after being fed thereto through entrance chute124. Additional. details of mills of this general type are described, ingreater detail in applicants co-pending application referred to above.

Rather than being provided with grate means through which the bulk of aproduct of a predetermined range of fine sizes is discharged as in theembodiment of mill shown in FIGS. 1 and 2, the mill 118 is of the typehaving an exit 126 of relatively large size extending coaxially ofsupporting trunnion 128, it being understood that the mill is rotatablysupported by apair of such trunnions which are mounted in suitablebearings not shown in order to simplify the illustration.

Extending preferably at an upwardly and inwardly inclined angle into thecircular exit opening 126 is a material discharge means comprising achute 130 provided at its upper entrance end with inlet sizing meanssuch as a series of spaced grate bars or grizzly 132. This grizzly willserve to prevent pieces in excess in silent the, spaces between thegrate bars 132 from entering'the chute 136.

This discharge chute 130 preferably is mounted for at least limitedpivotal movement about the axis of aligned trunnions 134, which arerotatable in bearings supported by base 136 which is stationarilysupported on a suitable foundation. Appropriate positioning means suchas for example, radial arm 138 having an arcuately slotted head 140 onthe outer end thereof is keyed or otherwise fixed at its upper end toone of the brackets 142 which is directly fixed to the chute 130. Ifdesired, a suitable scale 144 may be arranged on the head 140 forassociation with a fixed reference point 146 on base 136. Releasablelocking means such as a headed bolt 148 is disposed within the slot ofhead 140 and, when tightened, will hold said head as well as its arm 138and chute 130 in a desired fixed position to dispose the grizzly 132 inany one of a number of possible adjusted positions as shown in exemplarymanner by broken lines in FIG. 11.

When in a preferred position, the mixtures of friable material 150,while falling in various curved paths as illustrated in FIG. 11, willengage the grizzly 132, whereby the pieces of a size larger than thespaces between the bars of the grizzly will be deflected back into themill, while the material which will pass through said spaces will bedischarged by gravity along chute onto the classifier or screen 152.Eventually, the larger pieces of friable material which initially arerejected by grizzly 132 will be decreased in size by impact and abrasionuntil they finally pass through the grizzly. It also should beunderstood that while the grizzly 132 is desired in the preferredembodiment of the invention, the same may be dispensed.

with particularly under conditions where the maximum size of materialsupplied to the mill either in run-of-themine condition or otherwise isnot greatly in excess of the material which will pass through thegrizzly, or the chute 130 is moved sufiiciently to avoid all fallingpieces considered too large for use as pebbles.

The classifier or screen 152 in FIG. 10 is so illustrated here as toshow another of several well known arrangements of devices to classifyor divide material into different size components but, if desired, atrommel such as shown in FIG. 2 or other arrangement may be employed.

The separator or screen 152 has a plurality of spaced, parallel andsloping bars comprising a grate or grizzly 154. The spaces between thebars of the grizzly 154 will pass lumps or pieces of friable material ofwhich most are usually rounded by the time they are discharged from themill and which are minus 1 inch in minimum size. Pieces 156 which areminus 3 inch to plus 1 inch in size will be discharged in chute 158 forreturn to the mill by suitable means, not shown, but of the typeemployed in FIG. 1 for example, or for feed of such material either to asurge bin for delayed and controlled feed to an auxiliary or re-grindmill or for direct feed to an auxiliary mill in the manner describedabove relative to FIG. 1.

Another screen or grizzly 160 of 4 mesh size, for example, is mountedbelow the grizzly 154. Accordingly, the minus 1 inch to plus 4 mesh sizematerial 162 will pass along the top of screen or grizzly 160 and bedischarged into chute 164, while the minus 4 mesh to 0 size material 166will be discharged in the chute 167 and will constitute either finishedmaterial if of sufficiently fine size desired for certain uses or, ifotherwise desired, the chute 167 may communicate with the entrance of asecondary or re-grind mill such as the mill 86 of FIG. 1 or 116 of FIG.2 for example, for further reduction of the size of such material.

In autogenous mills of the type shown in FIGS. 10 and 11, it has beenfound that the larger pieces of friable material being processed in themill usually orbit within a path relatively close to the inner peripheryof the mill and, depending upon the speed of the mill, most usually willtravel somewhere approximately between the 6 oclock and 9 oclockpositions. Much of the material of intermediate and even fine sizes willorbit along with these larger pieces and gradually be reduced in size bythe larger pieces while said larger pieces themselves also are beingreduced in size. These smaller pieces of more intermediate size usuallywill rise to higher levels within the mill and, again depending upon thespeed of the mill and the size of these pieces, they may rise to the 10oclock or even the 12 oclock position of the mill as viewed relative toFIG. 11. With this material, a substantial part of the smaller sizesalso will be elevated for fall along curved paths such as illustrated inexemplary manner in FIG. 11. The material at the 11 oclock or, in somecircumstances, possibly even toward the 1 oclock position, dependingupon the speed of the mill, specific gravity of the material and size ofthe particles, will mainly be the smaller pieces and finer sizes.

In view of such orbiting of certain ranges of sizes at different zoneswithin a tumbling mill of this type, for

example, it will be seen that the chute 130 can be tiltably positionedto different positions and will receive mate- 9 rial of widely differentsize ranges, depending upon its location relative to the falling streamsor paths of material. The grizzly 132 may be of a replaceable nature soas to enable the grizzlies of different openings, as desired, to beused.

It will be further seen that, by reference to FIG. 11 particularly,suitably choosing the position of the grizzly 132 within the mill willavoid the same being struck by the very heavy pieces of material exceptoccasionally. Still further, if the grizzly and upper end of the chute13h are moved to the extreme permissible right-hand dotted line positionas illustrated in FIG. 11, only the finer segments of material will beencountered. Even more important is the fact that the position of thechute 130 and its grizzly 132 relative to the interior of the mill maybe adjusted while the mill is operating as, for example, when a changeoccurs in the nature, such as size consistency, of the material beingfed to the mill and, by adjusting the position of the chute 131i?suitably to meet the new conditions, maximum efiiciency of the mill canbe continued without stopping the mill.

In comparing the embodiment of primary mill and adjustable dischargemeans of FIGS. 10 or 11 with the mill 12 of the embodiments shown inFIGS. 1 and 2, it will be seen that the use of the grizzly 132 in theformer has a very similar effect to the adjustment of the radial spaces50 in the latter and the movement of the chute 130 in the former willproduce similar eifects as the removal of some of the lifting barsections 38 regarding amounts and relative location in the various zonesin the mill. However, these two embodiments principally are exemplary ofdesirable structures for the purpose of removing a desired amount ofcoarse, pebble material from a primary mill, together with finermaterial to be reduced further in size by said coarse material in asecond mill. Other structures to accomplish this purpose are conceivablewithin the spirit of the invention.

Generally in regard to the overall mill systems described above, as thesecondary or re-grind mill operates while employing friable grindingmedia produced by the primary mill and consisting of the same type ofmaterial as that being processed in both the primary and secondarymills, there will be a reduction in size not only of the intermediateand finer sizes of material within these mills but likewise a reductionin the friable grinding media pebbles or cobs themselves, whereby theirsupply must be replenished. Pebbles or cobs made up of the same materialas that being ground usually are not as hard as commercial flint pebblesor metal balls supplied from outside sources and will Wear down and beconsumed at a much greater rate. They must therefore be available inconsiderably greater quantities, which is the case in this instanceunless the material being ground is of a very unusual nature. It isobvious that if suitable grinding pebbles and cobs can be obtaineddirectly from the mill system itself without resorting to outsidesources, or the use of metal balls, the overall operation of the millsystem will be much more economical and of great advantage to the userof such a system as compared to those systems which require the use ofoutside sources of grinding media.

The various adjustments of certain elements of the mill system describedhereinabove have been referred to principally as being manual in nature.For example, this has been so in regard to regulation of the primarymill feed gate means 14, FIG. 1, the speed of the feed belt 16, theadjustment of the deflector plate or splitter 74, the positioning ofdeflector member or gate 100, as well as the speed of the pebble feedbelt 102 in the embodiment illustrated in FIG. 1. This invention alsocontemplates however the use of automatic means for main tainingoperating conditions at the optimum or at any other desired rate for thepurpose of reducing to a minimum the necessity for making manualadjustments after the system once has been set for a desired operationsuch as to produce a range of products wanted at a desired rate ofproduction. In considering the automatic adjustable means and methods ofemploying the same, several variables must be considered as well as thevmembers or parts of the mill system subject to adjustment to obtain theobjectives desired. In this regard, in practicing this invention, thefollowing exemplary com ponents may be employed in one form or anotherin the several systems described hereinabove and be adjusted to producedesired controlled operating characteristics for the entire mill system:

(1) The primary mill feed rate control means.

(2) The secondary or re-grind mill motor power differential underdifferent load conditions.

(3) The secondary or rc-grind mill sound level by which different loadconditions are observed.

(4) Pebble cobber quantity selector device, as well as pebble bin surgefeeder, if used, for controlling the rate of cobbing of pebbles andfeeding thereof to the secondary or re-grind mill.

(5) The rate of oversize or coarse component of secondary or re-grindmill discharge for controlling the overall output of the primary millcircuit and pebble cobbing or pebble feed rate to the secondary orre-grind mill, or combinations thereof.

(6) Other phenomena in the system, well known in the art, that also actin a manner that can be used to act on components so as to change themill operation.

It is known in the art of grinding in tumbling mills either of thecomplete or fully autogenous grinding type wherein all sizes arecomminuted simultaneously, or the partially autogenous grinding typewhich uses pebbles to grind relatively fine feed sizes, that among otherfactors the following conditions have influence upon the operations ofvarious mills, assuming the mills are first adjusted and operated at orreasonably close to their optimum capacity to deliver the desiredcharacter of product. With respect to the operation of the secondary orre-grind mill of the types of mill circuits or systems describedhereinabove, it has been found that:

(1) A decrease in sound indicates too much fine fraction of the materialin comparison to the coarse fraction thereof in the mill and that theproportion of fine fraction to coarse fraction is too high, as well aspossible coating of the lining.

(2) An increase in sound indicates an over supply of pebbles or adecrease in rate of feed or both.

(3) A decrease in normal power consumption can indicate either adecreased rate of pebble supply or possible overload of pebble charge.In this regard, this can result if the so-called normal mill load issuch as to be very close to that which will draw the maximum power thatcan be consumed by the mill.

(4) An increase in power over the so-called normal setting indicates agreater than normal pebble loading for a given power setting if saidsetting is sufficiently below the maximum power obtainable to allow someleeway.

(5) An increase in power and a simultaneous decrease in sound normallyindicates too great a pebble charge, together with too many fines in themill and/or possible coating of the lining.

(6) An increase in power and increase in sound normally indicates toomany pebbles and a deficiency of fine material.

(7) A decrease in power and decrease in sound can indicate eitherinsufiicient or possibly too many pebbles, it operated too close to themaximum power obtainable, and also possibly too high a percentage offine material.

(8) A decrease in power and increase in sound normally indicates adecrease in pebble charge if the normal power line is set sufiicientlybelow the maximum but, if this latter condition does not exist, saiddecrease in power and increase in sound could also indicate too great apeb- 11 ble charge. In either situation, a deficiency of fine materialalso is-indicated in the mill.

(9) An increase in the-rate of oversize from the secondary or re-grindmill indicates either too much feed to the primary mill as well as tothe secondary re-grind mill, or insuflicient pebbles in the secondaryre-grind mill and, under such circumstances, any increase of pebble feedrate to the secondary or re-grind mill will remove some of theintermediate size range from the primary mill and tendto balancethe loadin: the primary mill without changing primary mill feed rate, otherconditions being normal.

The aforementioned indices of the principal variables in the operationof the various components of the mill system. and the causes of suchcondition which have generally been determined from long experience, canbe employedin an additive or subtractive manner, automatically, tocorrect all but unusual conditions. These indices can be utilized tovary the component elements mentioned above, either simultaneously orseparately, as

conditionsdictate and do so automatically.

The particular characteristics of the overall operation,

such as feed conditions and other variables, are first ob'-' served, bymaking a'series of preliminary tests, and by using manual controls forobservation andcorrective purposes. The normal limitations are alsoestablished duringthis'period of manual control of the variousadjustable components and approximate optimum operating conditionsundervarious circumstances are noted and established. An exemplary controlcircuit for achieving automaticadjustment, regulation, and operation ofthe mill systems described hereinabove is illustrated in FIG. 12.

For example, in placing the mill system initially in operation, thefeeder for the primary mill is first adjusted so as to causethe mill tooperate normally under the conditions at hand. The pebble selector orsegregating mechanism'adjacent the exit of the primary mill in thecircuitsdescribed above are so adjusted that the pebbles cobbed fromitbeprimary mill arelfed to the secondary'or re-grind mill at approximatelythe desird rate, preferably to match the consumption of the pebblesduring'operation of the secondary mill. The contemplated principalcontrolling elements utilized to maintain conditions constant inthecircuit and particularly in the secondary or re-grind mill have beenselected to utilize sound, power consumption, andquantity of oversizeproduced by the secondary or re-grind mill,. as measured by suitablemeans. These three controlling elements or phenomena are examples ofoperating conditions which can be utilized to indicate certainconditions of the mill system and effect actuation of a circuit relaysystem when adjusted to function at the points desireds Other knownconditions and appropriate controlling means maybe used within thespirit of the-invention.

With respect to sound in the secondary mill, the functioningofthecircuit relay system would occur when the;

sound. reaches the noise level desired to be maintained. With respect tothe power consumption by the motor which drives the secondary mill, thecircuit relay system would function when a predetermined power input tothe motor islreached. Concerning the oversize produced by the secondarymill, the circuit relay system would be actuated when a predeterminedrate of production of oversize considered optimum for a given conditionis discharged from the secondary or re-grind mill.

The controllingcircuitry employed in the diagrammatic illustration ofFIG. 12 principally comprises standard components and includes suitablerelay systems, adjustable means to match any given condition desired,indicators, and time delay elements to eliminate fluttering or too rapidaction, particularly where there is a tendency for momentary variationswhen average conditions are desired. in this circuit, detaileddescription of each element is considered unnecessary, and generalreference to the various Inasmuch as standard elements are employedelements and the functions thereof is furnished to understand theoperation of the circuit as it is intended to be employed to control theprincipal variables automatically, after initial manual adjustment andsetting. The operation of the various feed mechanisms, sizing andsegregating mechanisms, as well as other elements of the overall millsystems, as described in detailhereinabove, arereferred to hereinafterin conjunction with the following detailed description of the circuitshown in FIG. 12.

Referring to FIGS. 1 and 12 specifically, there-is arranged in suitableposition relative to the secondary or re-grind mills 86 or 116 amicrophone 168 which is connected by a suitable circuit to sound controlunit 170. The power feed control circuit of the secondary mill drivingmotor 94 is connected to a power level control unit 172. The dischargefrom the secondary mill 86 passes to a suitable chute 174, see FIG. 1,for discharge onto separation means176 comprising an angularly disposedscreen 178, for example, of a desired mesh through which maximum sizesof fine product material will pass for discharge into product conduit180, for example.

The oversize portion of the product whichwill not pass through thescreen 178 is discharged onto suitable weighing means as indicated by atraveling belt 182 mounted on an indicating and weight recordingscaledevice of any suitable type well known in the art. Said belt dischargesinto achute 184 which delivers the oversize material either to othermeans outside of. the system or to suitable elevating means for returnto the primaryor initially, then by adjustment of the manuallycontrolled resistance 188 in the main control power line to themodulator190 and set to be just at thepoint of actuatingplate 74 throughlever 192 connected thereto by a link 193, and assumingfurther that allof the control elements are also adjustedso as to be just on thefunctioningor actuating point, then the degree of change desired betweenthe various controlling elements such as'element 170 responsive tosound, element 172 responsive to secondary mill power, and element 186responsive to the rate of oversize discharged from the secondary mill iscontrolled by resistances 194, 196 and 198 respectively. All of thesecontrol elements are correlated and each is variable. Each can beadjusted or eliminated from effect upon the circuit at will. Thevariability of these resistances makes it possible for the operator toselect the degree of change desired in the circuit of each controllingelement since one sensing element will usually have greater effect onthe circuitry than another, depending upon conditions.

If the pebble cobbing supplyis to be done solely by movement ofdeflector splitter 74 of segregating mechanism 56 of FIG. 1 and thepebbles are passed directly to secondary mill 86, switch 200 is then setso that line 264 is connected with line 231. However, if it is desiredto utilize surge bin 98, switch 200 then is altered to connect lines 292and 204, whereby the sensing elements than control pebble feeder motor206 which drives feed belt 102. When pebble feed from the surge bin isemployed, the pebble cobbing selector or deflector plate 74 is manuallycontrolled to maintain an adequate supply of pebbles in the surge binand is manually adjusted from time to time as conditions dictate. Gatedeflector member also is opened manually. The variable resistor 188 mayor may not be shunted out of the circuit when the system is adjusted forautomatic control at the will of the operator, depending onthe use ofone or more of the other resistors 194, 196, 198 which vary the degreeof control by sound element 170, secondary mill power element 172,

In the event that conditions within the overall grinding system are suchthat full normal operation can not be maintained due to excessivevariations in the primary mill feed characteristics that will have amajor effect on the pebble supply, a supplementary control isillustrated that will also control the primary mill feeder motor 20 ofthe embodiment shown in FIG. 1. This will help maintain the supply ofpebbles necessary to meet the requirements in the secondary mill circuitand will act in a supplementary manner to any other controlling elementswhich may normally control the primary mill as indicated generally bycircuit 232. These elements are not shown, but are well known in the artfor controlling the operation of the primary mill by the sound of thegrinding conditions therein, or the power consumed by the driving motorfor the primary mill, or other means. These latter control arrangementsare not part of the present invention, but the present invention doesillustrate means of further complementing the controls of the primarymill itself if they are desired.

The aforementioned auxiliary control of the primary mill feed rate isexemplified by contacts 208, 211 and 212, which operate in conjunctionwith the other contacts 233, 234 and 235 connected into the pebblecobbing control system, as described above, and in turn have their ownmeans of supplying the degree of change desired by resistances 214, Zl-land 213 which are also included in the circuitry for the motor 26 whichdrives the primary mill feeder. Any-one or all of the contactors may beconnected into or disconnected from the circuit at will by actuatingswitches 22%, 222, or 224 for the primary mill feed circuit, or switches236, 237 or 238 for the pebble feed cobbing circuit. The primary millfeeder motor speed, and hence, the feed rate, is regulated by controlunit 249 of conventional design and variable resistance 239complementary to or independent of the other motors 214, 216 and 218.

Under ordinary operating conditions, the sound of the I secondary orre-grind mill, through its control unit 170 and resistor circuit 194,normally controls the rate of feed of pebbles to said secondary millwhen the sound deviates from the preset sound level desired.Simultaneously, it can also control the feed rate to the primary mill ifswitch 220 is opened.

Power consumption by the secondary mill motor, by means of its controlunit 172, may be used to control the pebble feed to the secondary orre-grind mill if the power control resistor 196 is set primarily tooperate below the maximum power level. This unit can also be used tocontrol the primary mill feed rate if the switch 222 is opened.

The secondary mill oversize discharge rate, by means of its control unit186 and resistor 198, may be used to change the pebble feed rate to there-grinding mill under circumstances where the oversize rate dillersfrom the desired amount and said oversize discharge rate control canalso be set to alter the primary mill feed rate if switch 224 is opened.

It should be understood that under certain unusual conditions thematerial hardness or feed size range for the primary mill, with relationto the effect on the secondary or re-grind mill, might cause one or moreof the combinations of the controls to function differently than themanner outlined above. Provision is contemplated to reverse the controlfunctioning of any one or all of the elements used, if desired. Eachelement has a bearing upon the operation as a whole, and is so placed inthe circuit that it can be used or not used, as desired, and to anydegree desired, with relation to the other control elements, asillustrated, that may also be functioning at the same time. For example,sound control may be used and adjusted to allect the feed rate in anamount of 15%, for example, while another controlling element such asthe power consumption control unit, might only be adjusted to alfect thefeed rate in the amount of 5%, and still another element not be utilizedfor one reason or another which in many cases can only be determined bytrial. At the same time, for example, the oversize control circuit maybe arranged to alter the primary mill feed rate only, or it can at thesame time be so connected into the secondary mill circuit as toneutralize the ellect of the other control units by altering switch 241in the control unit 136 from a normally closed to a normally opensetting or vice versa.

To illustrate the manner of operation of the system, one of theinfluencing conditions affecting the milling circuit will be describedas an example. It is to be understood, however, that such illustrationshould be interpreted broadly and in accordance with the various otherconditions already outlined. For example, the mill system is firstadjusted to operate in a normal manner and the control devices alsoadjusted including the pebble cob deflector plate 74, which is properlyset to deliver the required amount of pebbles to the secondary mill.After a period of time, the mill power in mill 86 or 116 We will assume,for some reason, decreases. The signal to the power control circuit 172will also decrease, which, in turn, will cause relay 234 to close if itwere previously set to be in a normally open position. We will assume inthis case that only the mill motor power is being used in the automaticcontrolling circuit, in which case switch 237 will be open and switches236 and 238 closed. Switch 269 in the pebble supply circuit, when movedto the lower contact, will cause cobber control modulator 1% to besubjected to the signal caused by control unit 172 and specificallyrelay 234.

Closing of a circuit around resistance 1% will remove resistance 1% fromthe circuit. This increases the control signal which will, in turn,actuate modulator 1% to increase the pebble feed to the secondary mill.This can be accomplished if relay 234 is arranged to be normally open,as previously stated. We will also assume, for ex- I ample, resistance1% was set to change the signal strength by 10%. This will cause anequivalent alteration in the movement of cobber modulator 1%, and whenset so as to move the cobber plate '74 to increase the supply of pebbles76 to the secondary mill 86-416, this will increase the pebble load inthe mill and the mill motor power will gradually increase. So also willthe signal entering power control unit 172. When the relay 234 againopens, the current in the circuit energizing cobber modulator 19!?returns to that originally set and so also the cobber plate '74. Thiscycle will be repeated whenever the mill power again decreases, thus aso-called high-low adjustment is mades in the pebble supply. As statedpreviously, the operator by adjusting resistance 1% may control thedegree of change that will take place each time the relay closes.

Control by sound and also oversize may be made to operate the pebblecobbing modulating unit 1% in a like manner or a reverse manner,individually or cooperatively, as the case may be, in which case,switches 236 or 233 or both are opened. If all switches are opened, thenmill power, mill sound, and oversize are all in a position to controlthe modulator 198. If it is desired to control, for example, themodulator so as to decrease the pebble cobbing feed rate when theoversize increases, merely by changing relay 2.33 to the normally closedposition by moving switch 241 to the upper contact, as shown, thisobjective can be attained since now resistance 198 is removed from thecircuit, then added in when relay 233 opens, just the reverse of theother example, as described for the mill motor power control. The sameequivalent reversal effect is possible with the other two relays 23-5and 234, controlled by sound and power. It will be seen, as illustratedin these particular examples, that a normally open relay switch, whenclosed, increases the actuating control current signal, while a normallyclosed switch, when opened, will decrease the actuating control signal.

If for example the power control signal strength change was set at asstated in the previous example, and the oversize at 6%, then if bothcircuits were placed in operation and when both were being actuated thenet change in pebble cobbing rate would be 10% minus 6% or 4% increasein pebble cobbing rate.

It is obvious that an additive or subtractive effect can be obtained byuse of the various units set at various percentage changes in eitheracting separately or in combination, thus adding to or subtracting fromor partially nullifying the over-all degree of control by properactuation of the various switches 236', 237, 238, which, in turn, cut inor out, as the case may be, resistors 194, 196, 198. Instead ofcontrolling the pebble feed by the modulator 190, the same generaleffect can be achieved by turning switch 200 to the lower contact, inwhich case the pebble feeder motor 206 is actuated in like manner.

As to the control of feed to the primary mill through an operatingcondition of the secondary mill, a decrease, for example, of oversize inthe secondary mill can be made to increase the feed to the primary mill.If switch 224 is opened and after appropriate adjustment of resistors214 and 239, is made, and also relay 268 is arranged to be normally openso'that, when closed on a decrease in oversize, for example, resistor214 is shunted. When resistor 214 is shunted, this will increase theenergy going to the feed motor control unit 240, which in turn,increases the speed of the primary mill feeder motor, and hence, theprimary mill feed rate will be increased.

It is obvious also that simultaneous actuation of pebble feed to thesecondary mill and feed to the primary mill may be obtained byappropriate actuation of the various switches in the different controlcircuits.

The action that occurs in tumbling mills under various conditionsdiffers materially and what will affect power Very considerably in onesituation will not have any appreciable effect on the sound or oversizeproduced by the secondarymill, and vice versa. Those skilled in the artare familiar however with the fact that under certain conditionswhenhandling materials differing substantially in characteristics,- allthree or any one of the three aforementioned controlling elements,namely, sound, power consumption and oversize production, will varyconsiderably within the system and at times tend to be self compensatingand at others cumulatively coacting.

Furthermore, while the invention contemplates mainly the used anautogenous grinding mill as the preferred type of tumbling mill, suchmills may be a combination type of mill wherein other grinding media isemployed, at least in part, than the ore or material itself, such as bythe addition of balls, either into the primary or secondary millcircuit, as required or desired, and as sometimes is employed in millsof these types. While the size ranges mentioned may be considerednormal, a widely different selection of mesh sizes and pebble sizes isalso contemplated under various operating conditions. Still further,other means of removing portions of the coarser fractions or pebblesfrom the primary mill may be em-, ployed than those specificallyillustrated.

The action also contemplates the employment of wet grinding, as well asdry grinding, mill circuits. If the entire system is operated in aclosed circuit, normal circuitry will comprise the primary milloperating in its own closed circuit and the secondary mill operating inits own closed circuit; or the oversize from the secondary mill may bedelivered back to the primary mill, if desired, or only a portion of theintermediate products or sizes of either the primary or secondary millsmay be removed from the circuit entirely for separate treatment, asdesired.

It further is to be understood that other means of indicating theoperating conditions of the secondary or regrind mill than thosespecifically illustrated and described maybe employed, whereby thespecifically illustrated indicating and recording control and actuatingdevices shown in the system as a whole are to be regarded as exemplaryrather than restricting.

Although only a single secondary mill has been employed in the millsystem and processes described hereinabove, with the possible exceptionof the use of auxiliary mill 112 in the embodiment shown in FIG. 2, itis to be understood that the present invention contemplates the use ofadditional secondary mills respectively receiving material either fromthe primary mill and/or surge bin associated with the discharge thereof,or to receive material from the secondary mill presently illus trated inthe systems described hereinabove and illustrated in the drawings if theemployment of such additional secondary mills is found desirable andnecessary to the achievement of a desired product of some type of solidmaterial which may require the use of additional auxiliary millseventhough such additional auxiliary mills are not specifically illustratedin the drawings.

It is to be understood also that other means of operating a grindingcircuit are contemplated which utilize a plurality of control elementsas described in detail hereinabove, such for example, as in a situationwherein bin 98 is employed as the principal feed source for mill 86 anddoes not necessarily comprise a means solely for feeding pebbles. Undersuch circumstances, the control of the feed rate by feeder 102 then maybe affected by one or more of the elements of the overall control systemof FIG. 12, in combination or separately, as operating con ditions ofthe mill 86 dictate, to produce an integrated control for optimumresults.

Hereinabove and in the appended claims, the term autogenous is meant topertain to using the friable material undergoing reduction, either inWhole or in part, as its own grinding media. The term run-of-minematerial, as used hereinabove and in the appended claims, pertains to amixture of friable material which normally includes coarse, intermediateand fine sizes, the larger sizes being sufficient to reduce themselvesin size along with the other sizes present even though certain sizeranges may be eliminated or partially treated separately.

Although various embodiments of mill unit and systerns are described andillustrated, it is to be understood that while they have certain basicprinciples in common, they are not to be regarded as equivalents sincethey have different characteristics which lend them to functioningdifferently under various operating conditions and when treatingdifferent types of materials.

While the invention has been described and illustrated in its severalpreferred embodiments, it should be understood that the invention is notto be limited to the precise details herein illustrated and describedsince the same may be carried out in other ways falling within the scopeof the invention as claimed.

I claim:

1. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed solid friable material thereto for reduction into arange of sizes, segregating means arranged to receive at least some ofsaid friable material from said first mill and separate the same into aplurality of ranges of sizes including some coarse friable materialsuitable for use as grinding media, a second tumbling mill, and meansindependently of said second mill and operable to feed a desired amountof said segregated coarse friable material at a controlled rate to saidsecond mill to produce a desired grinding condition within said secondmill for friable material to be reduced in size therein.

2. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed solid friable material thereto for reduction into arange of sizes, segregating means arranged to receive at least some ofsaid friable material from said first mill and separate the same into aplurality of ranges of sizes including some coarse friable materialsuitable for use as grinding media, a second tumbling mill, andadjustable means independent of said second mill and operable to controlthe rate of feed of a desired range of sizes of said segregated friablematerial including a controlled amount of said coarse material to saidsecond mill and utilizing said coarse material as grinding media toproduce a desired grinding condition within said second mill formaterial to be reduced in size therein.

3. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed solid friable material thereto for reduction into arange of sizes, means operable to segregate said material from saidfirst mill into a plurality of ranges of sizes including some coarsefriable material suitable for use as grinding media, a second tumblingmill, means operable to feed one portion of said segregated coarsefriable material to said second mill to produce a desired grindingcondition within said second mill for reduction of material fed thereto,and means to return the other portion of said coarse friable materialfrom said segregating means back to the first tumbling mill for furtherreduction in size.

4. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed solid friable material thereto for reduction in sizeincluding a range of fine sizes, classifying means arranged to receivethe said material produced by said first mill and segregate the sameinto a plurality of ranges of sizes including some coarse friablematerial suitable for use as grinding media, a second tumbling mill,storage means operable to receive material partially reduced in size,means to feed at least some of said segregated coarse friable materialto said storage means, and adjustable means operable to feed a desiredamount of said segregated coarse friable material from said storagemeans to said second mill to produce a desired grinding conditiontherein for material fed thereto.

5. A tumbling type grinding mill system for subjecting a range of sizesof friable material to self-reduction of all sizes and comprising afirst tumbling mill, means to feed solid friable material thereto forsize reduction therein, adjustable material handling means operable toreceive said material from said first mill and segregate the same into aplurality of size ranges including a coarse range of friable materialsuitable for use as grinding media, a second tumbling mill, and meansoperable to feed to said second mill desired proportions of saidsegregated ranges of friable coarse sizes at a desired rate controlledby the adjustment of said material handling means to produce a desiredgrinding condition within said second mill for reduction in size ofmaterial fed thereto.

6. A tumbling type grinding mill system for subjecting a range of sizesof friable material to self-reduction of all sizes and comprising afirst tumbling mill, means to feed solid friable material thereto forreduction to a range of mixed sizes, adjustable material handling meansperable to receive material from said first mill and segregate the sameinto a plurality of size ranges including a coarse range of friablematerial suitable for use as grinding media, a second tumbling mill, andmeans responsive to an operating condition of said second mill andoperable to adjust said material handling means to cause the de liveryof desired proportions of said segregated size ranges of material tosaid second mill, said segregated size ranges including a proportion ofsaid coarse range to produce a desired grinding condition within saidsecond mill for material fed thereto.

7. A tumbling type grinding mill system for subjecting a range of sizesof friable material to self-reduction of all sizes and comprising afirst tumbling mill, means to feed solid friable material thereto forreduction to a range of mixed sizes, adjustable material handling meansoperable to receive said material from said first mill and segregate thesame into a plurality of size ranges including a coarse range of friablematerial suitable for use as grinding media, a second tumbling mill, andmeans responsive to the sound of said second mill during grindingoperation thereof and operable to adjust said material handling means tocause the delivery of desired proportions of said segregated size rangesof material to said second mill and including a controlled proportion ofsaid coarse range to produce a desired grinding condition within saidsecond mill for material fed thereto.

8. A tumbling type grinding mill system for subjecting a range of sizesof friable material to self-reduction of all sizes and comprising afirst tumbling mill, means to feed solid friable material thereto forreduction to a range of mixed sizes, adjustable material handling meansoperable to receive said material from said first mill and segregate thesame into a plurality of size ranges including a coarse range of friablematerial suitable for use as grinding media, a second tumbling mi-ll,power means to drive said latter mill, and means responsive to the powerconsumption of said second mill and operable to adjust said materialhandling means to cause delivery of desired proportions of saidsegregated size ranges to said second mill and including controlledproportions of said coarse range to produce a desired grinding conditionWithin said second mill for material fed thereto for reduction in sizetherein.

9. A tumbling type grinding mill system for subjecting a range of sizesof friable material to self-reduction of all sizes and comprising afirst tumbling mill, means to feed solid friable material thereto forreduction to a range of mixed sizes, adjustable material handling meansoperable to receive said material from said first mill and segregate thesame into a plurality of ranges of sizes including a coarse range offriable material suitable for use as grinding media, a second tumblingmill, means responsive to the quantity of oversize material dischargedfrom said second tumbling mill and operable to adjust said materialhandling means to cause the delivery of desired proportions of saidsegregated size ranges of products from said first tumbling mill to saidsecond mill and including a controlled amount of said coarse range toproduce a desired grinding condition within said second mill formaterial fed thereto.

10. A tumbling type grinding mill system for subjecting a range of sizesof friable material to self-reduction of all sizes and comprising afirst tumbling mill, means to feed solid friable material thereto forreduction to a range of mixed sizes, material handling means operable toreceive material from said first mill and segregate the same into aplurality of size ranges including a coarse range of friable materialsuitable for use as grinding media, asecond tumbling mill, adjustablemeans operable to cause the delivery of desired proportions of saidsegregated size ranges to said second mill and including a desiredcontrolled proportion of said coarse range to produce a desired grindingcondition Within said second mill for material fed thereto to produce arange of fine products of predetermined size range and oversize coarserproducts and discharge the same therefrom, means operable to separatesaid coarser oversize product material from said range of fine products,and means responsive to the quantity of coarser product produced by saidsecond mill to control the adjustment of said adjustable delivery meansfor said second mill.

11. A grinding mill system comprising a first tumbling mill operable toreceive and subject a range of sizes of friable material toself-reduction by tumbling the same autogenously within said mill, saidmill having entrance and exit means, size-limiting screening meansadjacent said exit means and operable to control the sizes of materialdischarged from the grinding zone of the mill, the majority of theopenings of said screening means being of a size to permit passagetherethrough of a predetermined maximum size of fine and intermediatesizes of material and capable of discharging therethrough the majorityof the output of said mill, said screening means also including a minornumber of discharge openings substantially larger in size than saidmajority of openings and comprising a minor percentage of the totalscreen opening area and operable to discharge from said grinding zone anamount of coarse pieces of material capable of serving as grinding mediathat is less than the percentage of fine and intermediate sizes ofmaterial discharged through said screening means, means to receive fromsaid screening means said mixture of fine and intermediate sizes ofmaterial and minor percentage of coarse pieces of friable grinding mediaand operable to segregate said coarse pieces from said fine andintermediate sizes of material and also separate said fine sizes fromsaid intermediate sizes, a second tumbling mill, means operable to feeda desired amount of said segregated coarse pieces to said second mill,and means operable to return said intermediate sizes of material and anyexcess segregated coarse pieces of material to said first mill forfurther reduction in size.

12. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed solid friable material thereto for reduction to arange of sizes, said first tumbling mill having means to discharge arange of smaller size material and adjustable outlet means operable toregulate the rate of discharge from said mill of a restricted amount ofa range of relatively coarse friable material of predetermined maximumsize capable of serving as grinding media, a second tumbling mill, andmeans to feed said range of coarse sizes of friable material to saidsecond mill to produce a desired grinding condition within said secondmill for said smaller material fed thereto for reduction in sizetherein.

13. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed solid friable material thereto for reduction to arange of sizes, said first tumbling mill having outlet means operable toprevent discharge of material from said mill in excess of apredetermined maximum size, material handling means operable to receiveand segregate all the product material discharged therefrom into sizeranges of predetermined limits and discharge from said material handlingmeans an adiusted restricted amount of such ranges of material includinga range of relatively coarse sizes of predetermined maximum size capableof serving as grinding media, a second tumbling mill, and adjustablemeans operable to feed from said discharged material regulated 'desiredproportions of said segregated size ranges of material to said secondmill to produce a desired grinding condition within said second mill forsaid material fed thereto.

14. A grinding mill system comprising a first tumbling mill, means tofeed solid friable material thereto for reduction to a range of sizes,segregating means arranged to receive such material from said first milland separate the same into a plurality of ranges of sizes including somecoarse sizes suitable to serve as grinding media, a second tumblingmill, a storage bin, means operable selectively to feed desiredproportions of said coarse sizes directly to said second mill and tosaid storage bin for controlled feed to said second mill as required bythe grinding operations of said second mill to produce a desiredgrinding condition therein utilizing said coarse sizes as grinding mediaand producing a desired range of fine products, and conducting meansextending between said segregating means and the entrance of said firstmill and operable to conduct excess coarse sizes of material back tosaid first mill for further reduction in size.

15. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed run-ofmine raw solid friable material to said millat variable rates for reduction into a range of sizes, means to controlsaid feed of raw material to said mill, segregating and classifyingmeans operable to receive material from said first mill and separatetherefrom a range of relatively coarse friable material suitable for useas grinding media, a second tumbling mill, feed means for said secondmill operable to feed said separated range of coarse friable materialthereto at a predetermined controlled rate to produce a desired grindingcondition within said second mill for material fed thereto, and feedcontrol means for said second mill interconnected to said feed controlmeans for said first mill and operable to control the rate of feed ofsaid raw material thereto.

16. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed run-ofmine raw solid friable material to said millat variable rates for reduction into a range of sizes, segregating andclassifying means operable to receive material from said first mill andseparate therefrom a range of relatively coarse friable materialsuitable for use as grinding media, a second tumbling mill, feed meansfor said second mill operable to feed said separated range of coarsefriable material thereto at a predetermined controlled rate to produce adesired grinding condition within said second mill for material fedthereto from said first mill for further processing, and control meansfor said feed means for said first mill responsive to an operatingcondition of said second mill and operable thereby to vary the rate offeed of raw material to said first mill in accordance with saidoperating condition of said second mill.

17. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed run-ofmine raw solid friable material to said millat variable rates for reduction into a range of sizes, segregating andclassifying means operable to receive material from said first mill andseparate therefrom a range of relatively coarse friable materialsuitable for use as grinding media, a second tumbling mill, feed meansfor said second mill operable to feed said separated range of coarsematerial thereto at a predetermined controlled rate to produce a desiredgrinding condition within said second mill for material fed thereto fromsaid first mill for further processing, and control means for said feedmeans for said first mill responsive to the operating sound of saidsecond mill and operable thereby to vary the rate of feed of rawmaterial to said first mill in accordance with the sound of saidoperating condition of said second mill.

18. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed run-ofmine raw solid friable material to said millat variable rates for reduction into a range of sizes, segregating andclassifying means operable to receive material from said first mill andseparate therefrom a range of relatively coarse friable materialsuitable for use as grinding media, a second tumbling mill, feed meansfor said second mill operable to feed said separated range of coarsefriable material thereto at a predetermined controlled rate to produce adesired grinding condition within said second mill for material fedthereto, and control means for said feed means for said first millresponsive to the consumption of operating power by said second mill andoperable thereby to vary the rate of feed of raw material to said firstmill in accordance with said consumption of operating power by saidsecond mill.

19. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed run-ofmine raw solid friable material to said millat variable rates for reduction into a range of sizes, segregating andclassifying means operable to receive material from said first mill andseparate therefrom a range of relatively coarse friable materialsuitable for use as grinding media, a second tumbling mill, feed meansfor said second mill operable to feed said separated range of coarsefriable material thereto at a predetermined controlled rate to produce adesired grinding condition within said second mill for material fedthereto, and control means for said feed means for said first millresponsive to the quantity of material in excess of a predetermined sizeproduced by said second mill and operable thereby to vary the rate offeed of raw material to said first mill in accordance with said excessmaterial condition of said second mill.

20. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a firstcomminuting mill, means to feed solid friable material thereto forreduction to a mixed range of sizes, means positioned and operable toreceive material from said first mill and segregate the same into aplurality of ranges of sizes including a substantially coarse range offriable product suitable to serve as grinding media, a secondcomminuting mill of the tumbling type, means to feed at least some ofsaid segregated coarse range of friable product to said second mill of acontrolled rate adequate to produce a desired grinding condition thereinfor material fed thereto to produce a desired range of products, and athird comminuting mill operable to receive from said first mill anundesired proportion of said segregation ranges of sizes for furthercomminution within said third mill.

21. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a firstcomminuting mill, means to feed solid friable material thereto forreduction to mixed ranges of size from fine to coarse, means positionedand operable to receive said mixed friable material from said first milland operable to segregate the same into separated ranges of sizesincluding fine, intermediate and coarse, said coarse range of friablematerial being suitable to serve as grinding media, a second comminutingmill of the tumbling type, means to feed to said second mill saidsegregated fine range and at least some of said coarse range of productat a controlled rate to produce a desired grinding condition therein forfurther reducing said fine material in size, a third comminuting mill,and means to deliver from said first mill to said third mill thesegregated intermediate range of material for further comminutiontherein to finer sizes.

22. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a firstcomminuting mill, means to feed solid friable material thereto forreduction to mixed ranges of size from fine to coarse, means positionedand operable to receive said mixed friable material from said first milland operable to segregate the same into separated ranges of sizesincluding fine, intermediate and coarse, said coarse range of friablematerial being suitable to serve as grinding media, a second comminutingmill of the tumbling type, means to feed to said second mill saidsegregated fine range and at least some of said coarse range of productat a controlled rate to produce a desired grinding condition therein forfurther reducing said fine material in size, a third comminuting mill,means to deliver from said first mill to said third mill the segregatedintermediate range of material for further comminution therein to finersizes, and means to deliver said further comminuted material from saidthird mill to said second mill for still further comminution therein bythe coarser material in said second mill.

23. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed solid friable material thereto for reduction in sizethereof, and discharge means positioned relative to the grinding zone ofsaid mill to effect discharge of ground and semiground friable materialand said discharge means also including means forming passage openingsof a size adequate to permit discharge from the mill of coarse friablepebble material larger than said ground and semiground material andsuitable for use as grinding media, said means forming passage openingsalso being variable in position relative to said mill to afforddischarge of a regulated desired quantity of said coarse friablematerial for use as grinding media in a second mill.

24. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed solid friable material thereto for reduction into arange of sizes, discharge means operable relative to the interior ofsaid mill to effect discharge from the mill of ground and semi-groundfriable material of a predetermined maximum size, and additional meansforming discharge passage openings of a size adequate to permitdischarge from the mill of coarse friable material larger than saidground and semi-ground material and suitable for use as grinding media,said additional means forming discharge passage openings being variablein extent, whereby the total area of said passage openings beingvariable to effect discharge of a desired quantity of said coarsefriable material from said mill for use in a second mill.

25. A grinding m-ill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, means to feed solid friable material thereto for reduction into arange of sizes, discharge means operable relative to said mill to elfectdischarge from the mill of ground and semi-ground friable material of apredetermined maximum size, and additional discharge means formingdischarge openings and being variable in position within said mill toposition said openings Where desired and said openings being of a sizeadequate to permit discharge from the mill of coarse friable materiallarger than said ground and semi-ground material and suitable for use asgrinding media, the total area of said discharge openings also beingvariable and in conjunction with the variable positioning of saiddischarge openings effect-ing discharge of a quantity of said coarsematerial to be fed to a second mill, and means operable to deliver asufficient amount of said coarse material to a second mill to produce adesired grinding condition therein for reduction of material fedthereto.

26. A grinding mill system comprising a first tumbling mill, means tofeed solid friable material thereto for re duction into a range ofsizes, discharge grate sections operable to permit passage of ground andsemi-ground friable material of a predetermined maximum size from saidmill, said grate sections having passage openings therebetween which arelarger than the openings Within said grate sections to permit exitingfrom the mill of an amount of coarse friable material larger than thatwhich passes through said grate openings and suitable for use asgrinding media, means selectably positionable within said passageopenings between said grate sections to cover portions of said openingsat selected locations relative to said grate sections, thereby to effectdischarge of a desired quantity of said coarse material to be fed to asecond mill, and means operable to deliver said desired quantity ofcoarse friable material to a second mill to produce a desired grindingcondition within said second mill for reduction of material fed thereto.

27. A grinding mill system comprising a first tumbling mill havingentrance and exit means, means to feedsolid material thereto forreduction to a range of mixed sizes, material discharge means extendinginto and adjustably positionable Within said mill with the inner endthereof arranged to receive a selected portion of a mixture of saidground and partially ground material While the same tumbles in saidmill, the average size and amount received being variable and inaccordance With the adjusted position of said discharge means Withinsaid mill and the larger sizes of said material being capable of servingas grinding media for the smaller sizes, a second tumbling mill, andmeans to feed said mixture of material received by said discharge meansto said second mill 23 to produce a desired grinding condition thereinfor said material fed thereto.

28. An autogenous grinding mill system comprising a first tumbling millhaving entrance and exit means, means to feed solid material thereto forreduction to a range of mixed sizes, material discharge means extendinginto said mill and operable to receive material while falling withinsaid mill during tumbling thereof and operable to conduct the materialfalling thereon through said exit, segregating means arranged to receivethe material discharged from the first mill by said material dischargemeans and classify the same into a plurality of ranges of sizesincluding a substantially coarse range of predetermined maximum size andcapable of serving as a grinding media, a second tumbling mill, andmeans to feed desired selected proportions of said classified ranges ofsizes of material including at least a portion of said coarse range tosaid second mill to produce a desired grinding condition within saidsecond mill for said material fed thereto.

29. An autogenous grinding mill system comprising a first tumbling millhaving entrance and exit means, means to feed solid material thereto forreduction to a range of mixed sizes, material discharge means extendinginto said mill and the inner end thereof being adjustably positionableWithin said mill to receive material from a selected location whilefalling within said mill during tumbling and conduct the same throughthe exit of said mill, segregating means arranged to receive materialfrom said material discharge means and classify the same into aplurality of ranges of sizes including a substantially coarse rangecapable of serving as a grinding media, a second tumbling mill, andmeans to feed desired selected proportions of said classified ranges ofsize of material including said coarse range to said second mill toproduce a desired grinding condition within said second mill for saidmaterial fed thereto.

30. A grinding mill system comprising a tumbling mill, means to feedsolid material thereto for reduction, a discharge chute extending at oneend into said mill and operable to receive ground and also semi-groundmaterial of larger size while tumbling therein, and means movablysupporting said discharge chute relative to said mill to effectselective positioning of the inner end thereof relative to said mill toeffect selected restrictive discharge of amounts and sizes of materialfrom a selected position within said mill.

31. A grinding mill system comprising a tumbling mill, means to feedsolid material thereto for reduction, and material discharge means insaid mill having adjustable means forming exit openings which arevariable in total area and thereby operable to permit a selectiverestricted discharge of material of larger size.

32. An autogenous grinding mill system comprising a first tumbling mill,means to feed solid material thereto for reduction to a range of mixedsizes, material discharge means including a first restricting meansoperable to permit relatively small sizes of material of predeterminedmaximum size to pass from said mill and a second restricting meansoperable to permit larger sizes of material of predetermined maximumsize capable of serving as a grinding media to be discharged from saidmill and said second restricting means being variable to causeselectively different amounts of said larger sizes of material to bedischarged, a second tumbling mill, and means to feed desired selectiveproportions of said relatively large sizes of material to said secondmill together with said relatively small sizes to produce a desiredgrinding condition within said second mill for said material fedthereto.

33. An autogenous grinding mill system comprising a first tumbling mill,means to feed solid material thereto for reduction to a range of mixedsizes, material discharge means including sizing means having openingsoperable to permit removal of ranges of relatively fine material fromthe mill and discharge openings substantially larger than the openingsof said sizing means operable to permit discharge of a substantallycoarse range of material substantially larger than said relatively finematerial and capable of serving as a grinding media and determine themaximum size thereof, a second tumbling mill, means operable to feeddesired proportions of said ranges of relatively fine and coarsematerial to said second mill to produce a desired grinding conditionWithin said mill for said material fed thereto, and means operable tovary the extent of said larger discharge openings to effect discharge ofa predetermined proportion of said coarse range of material from saidfirst mill for use in said second mill.

34. An autogenous grinding mill system comprising a first tumbling mill,means to feed solid material thereto for reduction to a range of mixedsizes, material discharge means including sizing means having openingsoperable to permit removal of ranges of relatively small sizes ofmaterial from the mill and discharge openings substantially larger thanthe openings of said sizing means operable to permit discharge of asubstantially coarse range of material substantially larger than saidsmall sizes of material and capable of serving as a grinding media anddetermine the maximum size thereof, a second tumbling mill, meansoperable to feed desired portions of said ranges of small sizes andcoarse material to said second mill to produce a desired grindingcondition within said second mill for said material fed, and closuremeans positionable over selected extents of said larger dischargeopenings and at selected positions thereof within the grinding zone ofsaid first mill to effect discharge of a predetermined proportion ofsaid coarse range of material from selected grinding zones of said firstmill for use in said second mill.

35. An autogenous grinding mill system comprising a first tumbling mill,means to feed solid material thereto for reduction to a range of mixedsizes, material discharge means including apertured sizing means withinsaid mill operable to remove from the grinding zone of said mill rangesof relatively small material the maximum size of which is controlled bysaid sizing means, exit means for said mill, segregating means exteriorof said mill arranged to receive from said exit material of larger sizethan said relatively small material and operable to separate from saidlarger size material a substantially coarse range of predeterminedmaximum size capable of serving as a grinding media, a second tumblingmill, and means to feed desired proportions of said classified ranges ofcoarse sizes of products to said second mill together with saidrelatively fine sizes to produce a desired grinding condition withinsaid second mill for said material fed thereto.

36. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a tumbling mill,adjustable feed means operable to deliver solid friable material to saidmill at a desired rate for reduction in size thereby and producingvarious operating conditions in said mill, a plurality of adjustablecontrol means for said feed means respectively responsive to saiddilferent operating conditions of said mill, a control circuit for saidmill system, and means in said circuit operable to integrate thefunctional results of said plurality of adjustable control means toproduce a composite resultant operation of said feed means which willproduce a desired optimum grinding condition in said mill.

37. A grinding mill system for subjecting a range of sizes of friablematerial to self-reduction of all sizes and comprising a first tumblingmill, adjustable feed means operable to feed solid friable material tosaid mill at a desired rate for reduction in size thereof, means todischarge from said mil ranges of relatively fine sizes of material ofpredetermined maximum size and a range of relatively coarse sizematerial capable of serving as grinding pebble media, a second tumblingmill, and adjustable means to feed said grinding pebble media to saidsecond tumbling mill at a regulated rate operable to grind materialwithin said second mill at an optimum reduction rate while producingvarious operating conditions in said second mill, a control circuit forsaid mill system, a plurality of control means for said feed means forsaid mills connected in said circuit and responsive to said variousoperating conditions in said second mill, and means in said controlcircuit operable to integrate the functional results of said pluralityof adjustable control means to produce a composite resultant control ofsaid feed means for said mills which will maintain said optimumreduction rate of material in said second mill.

38. A process of grinding solid friable run-of-mine raw material toeffect simultaneous self-reduction of all sizes thereof and comprisingthe steps of subjecting the raw material to autogenous grinding actionin a primary mill to reduce the size of the pieces and particlesthereof, removing from said mill a desired range of the larger sizes ofsaid pieces not exceeding a predetermined maximum size and capable ofserving as friable grinding media, and introducing into a secondtumbling mill a selected proportion of said removed pieces at acontrolled rate suitable to produce optimum grinding results therein andutilizing said friable pieces fed to said second mill as grinding mediafor material in said mill to produce autogenously therefrom a desiredrange of finer sizes of ground product material.

39. A process of grinding solid friable runof-mine raw material toeffect simultaneous self-reduction of all sizes thereof and comprisingthe steps of subjecting the raw material to autogenous grinding actionin a primary mill to reduce the size of the pieces and particlesthereof, removing from said mill a desired range of the larger sizes ofsaid pieces not exceeding a predetermined maximum size and capable ofserving as friable grinding media, introducing into a second tumblingmill a selected proportion of said removed pieces at a controlled ratesuitable to produce optimum grinding results therein and utilizing saidfriable pieces fed to said second mill as grinding media for material insaid mill to produce autogenously therefrom a desired range of finersizes of ground product material, and returning the non-selected rangeof larger sizes of material to the primary mill for further reduction insize.

40. A process of grinding solid friable run-of-mine raw material toeffect simultaneous self reduction of all sizes thereof comprising thesteps of subjecting the raw material to autogenous grinding action in aprimary mill to reduce the size of the pieces and particles thereof,removing from said mill a desired range of relatively coarse sizes ofsaid pieces capable of serving as friable grinding media, introducing adesired amount of said removed relatively coarse friable pieces into asecond tumbling mill at a controlled rate and utilizing said pieces insaid second mill as friable grinding media for material in said mill toproduce a desired range of ground product material, grinding theundesired relatively coarse friable material in a third mill to reducethe size thereof to a desired range of smaller sizes, and feeding thelatter range of smaller size material to said second tumbling mill forfurther reduction to produce a range of relatively fine product size.

41. A process of grinding solid friable run-of-mine raw material ofvarious sizes autogenously to reduce the size thereof simultaneously toranges of finer sizes and comprising the steps of subjecting the rawmaterial to primary tumbling in a mill to reduce the size of the piecesand particles of said raw material, discharging the products of saidmill and segregating from said discharged products the finer size rangesof predetermined maximum size and a desired range of relatively coarsesizes of said pieces of predetermined maximum size capable of serving asfriable grinding media, feeding said finer ranges of said dischargedproducts to a second tumbling mill, and also introducing into saidsecond tumbling mill a controlled amount of said relatively coarse rangeof friable material sufiicient to produce a desired optimum grindingeffect in said second mill further to reduce the size of the finer sizeranges of products fed thereto from said primary mill and therebyproduce a controlled range of desired fine products.

42. A process of grinding friable run-of-mine material of various sizesto reduce all sizes thereof simultaneously to a range of fine sizes andcomprising the steps of subjecting the raw material to tumbling in aprimary mill to reduce the size of the material autogenously, removingfrom said mill a desired range of relatively coarse sizes of said piecescapable of serving as friable grinding media, removing smaller sizes ofthe products from said primary mill and subjecting said smaller sizes totumbling and grinding in a second mill by a controlled amount of saidrelatively coarse pieces of friable material to produce at optimumefficiency a desired range of fine particle products, and controllingthe amount of relatively coarse friable material fed to said second millin accordance with an operating condition within said second mill.

43. A process of grinding friable run-of-mine raw material of varioussizes to reduce all sizes thereof simultaneously to a desired range offine products and comprising the steps of subjecting the raw material togrinding within a primary tumbling mill to reduce the size of saidmaterial to various sizes including a coarse range of sizes suitable foruse as a friable grinding media and finer sizes, removing the groundproducts from said mill, feeding the finer sizes of said ground productsand a controlled proportion of the said coarse size pieces to a secondtumbling mill for use as grinding media for the smaller sizes ofmaterial fed to said second tumbling mill, and controlling theproportion of coarse size pieces fed to said second mill in accordancewith the sound of grinding conditions within said second mill.

44. A process of grinding friable run-of-mine raw material of varioussizes to a desired range of fine products comprising the steps ofsubjecting said raw material to tumbling in a primary mill to reducesaid material autogenously to various sizes including a range of coarsefriable pieces capable of serving as grinding media and finer sizes,removing the ground products from said primary mill, feeding the finersizes and a controlled proportion of said coarse range of pieces ofmaterial to a second tumbling mill and utilizing said coarse friablepieces therein to produce a controlled desired range of fine particleproducts, and controlling the proportion of said coarse pieces ofmaterial fed to said second mill in accordance with the power consumedto drive said second mill.

45. A process of grinding friable run-of-mine raw material of varioussizes to a desired range of fine products comprising the steps ofsubjecting said raw material to tumbling in a primary mill to reducesaid material autogenously to various sizes including a range of coarsefriable pieces capable of serving as grinding media and finer sizes,removing said ground material from said primary mill, feeding the finersizes and a controlled proportion of said coarse range of pieces to asecond tumbling mill and utilizing said coarse friable pieces therein toproduce a controlled desired range of fine particle prod nets, andcontrolling the proportion of coarse pieces of material fed to saidsecond mill in accordance with the amount of oversize product materialproduced by said.

second mill.

46. A process of grinding friable raw solid material of various sizes toreduce the size thereof to a range of fine sizes comprising the steps ofsubjecting the material to autogenous grinding in a primary mill toreduce the size of said raw material, retaining within the mill allmaterial in excess of a predetermined maximum size, removing from saidmill a predetermined maximum size of 'relatively fine ground product anda relatively coarse size of friable product of predetermined maximumsize selected from a desired grinding zone of said primary mill andsuitable for use as grinding media, feeding said removed sizes ofmaterial to a second tumbling mill for further reduction of saidrelatively fine ground product by said coarse size of product whileusing a controlled proportion of the relatively coarse product which issmaller than the proportion of relatively fine ground product, andtumbling the said controlled proportions of relatively fine and coarsematerial in said mill to grind the fine material fed to said secondarymill to a desired range of finer sized product.

47. A process of grinding friable run-of-mine material to reduce thesize thereof to a desired range of fine sizes, said process comprisingthe steps of subjecting the raw material to autogenous grinding bytumbling in a primary autogenous grinding mill to reduce the sizethereof, selecting a grinding zone thereof for removal of a range ofcomminuted products from said mill comprising a desired relatively largeproportion of ground and partially ground relatively fine products and asmaller proportion of relatively coarse size friable pieces suitable foruse as grinding media for said relatively fine products, segregatingsai'd relatively coarse and fine size ranges, and feeding said removedrelatively fine products to a second tumbling mill and also feeding saidcoarse size pieces to said second tumbling mill at a controlled rate tooperate therein as grinding media for the relatively fine prod ucts,thereby producing desired controlled grinding conditions within saidsecond mill to produce a desired range of fine products.

48. A process of grinding raw solid friable material of various sizes toproduce a range of fine products comprising the steps of subjecting suchraw material to tumbling in a primary mill to reduce the size of saidmaterial to a mixture including a desired range of fine sizes,subjecting the products of said mill to sizing and removing from saidmill a range of fine products of maximum size controlled by said sizing,selecting a desired range of relatively coarse pieces of material fromsaid primary mill capable of serving as friable grinding media for saidfine products and removing the same from said mill through dischargeopenings therein, feeding to a second tumbling mill said fine productsand a desired smaller proportion of said coarse friable pieces at acontrolled rate and utilizing said coarse pieces therein as grindingmedia to reduce said fine sizes of material to a controlled desiredrange of finer particle products, and controlling the proportion of saidcoarse pieces to be fed to said second mill by selecting the size andtotal area of discharging openings in said primary mill through whichsaid coarse pieces of material exit therefrom.

49. A process for reducing the size of solid friable material byautogenous tumbling action within a mill capable of developing a numberof different operating conditions and comprising the steps of feedingmaterial to said mill at a rate to produce optimum autogenous grindingconditions within said mill for the material fed thereto, said ratebeing determined by integrating the results of said dilferent operatingconditions of said mill as said material is ground autogenously therebyto produce a collective resultant to effect any adjustment of the feedrate which may be necessary to achieve said optimum rate of feed forsaid mill.

50. A grinding mill mounted for rotation to effect re d'uction in sizeof friable material autogenously by tumbling, said mill having adiameter appreciably greater than the length thereof and being providedwith means operable to elevate and mix laterally the mass of materialundergoing treatment, means to feed solid material to said mill, andmaterial discharge means extending laterally into the grinding zone ofthe mill and having receiving means positioned within said grindingzoneof the mill to intercept and receive a portion of the mixture ofground material of various sizes while the same is tumbling within themill, said means being operable to restrict the discharge to apredetermined maximum size, whereby the oversize material remains in themill for further reduction in size.

References Cited in the file of this patent UNITED STATES PATENTS1,673,891 Stehli June 19, 1928 2,235,928 Hardinge Mar. 25, 19412,269,912 Ladoo et al. Ian. 13, 1942 2,332,701 Dowsett Oct. 26, 19432,381,351 Hardinge Aug. 7, 1945 2,491,466 Adams Dec. 20, 1949 2,766,941Weston Oct. 16, 1956 OTHER REFERENCES A. W. Fahrenwalds 1933 Rock Mill,Engineering and Mining Journal, volume 163, Number 5, page 83, May 1962.

38. A PROCESS OF GRINDING SOLID FRIABLE RUN-OF-MINE RAW MATERIAL TOEFFECT SIMULTANEOUS SELF-REDUCTION OF ALL SIZES THEREOF AND COMPRISINGTHE STEPS OF SUBJECTING THE RAW MATERIAL TO AUTOGENOUS GRINDING ACTIONIN A PRIMARY MILL TO REDUCE THE SIZE OF THE PIECES AND PARTICLESTHEREOF, REMOVING FROM SAID MILL A DESIRED RANGE OF THE LARGER SIZES OFSAID PIECES NOT EXCEEDING A PREDETERMINED MAXIMUM SIZE AND CAPABLE OFSERVING AS FRIABLE GRINDING MEDIA, AND INTRODUCING INTO A SECONDTUMBLING MILL A SELECTED PROPORTION OF SAID REMOVED PIECES AT ACONTROLLED RATE SUITABLE TO PRODUCE OPTIMUM GRINDING RESULTS THEREIN ANDUTILIZING SAID FRIABLE PIECES FED TO SAID SECOND MILL AS GRINDING MEDIAFOR MATERIAL IN SAID MILL TO PRODUCE AU-